This invention relates generally to sheet separators and more particularly to a sheet separator and method for separating doublets as they are advanced through an area of a machine, e.g., a copying machine.
Separation of double sheets of paper is useful for jam prevention or shutdown of machines which handle individual paper sheets, such as copying machines. In the sheet handling operation of copying machines, it is extremely important that not more than a single copy sheet be fed to the photoconductor at a time because to do so could cause damage to the photoconductor as well as waste of paper and operator time in having to go into the machine and remove jammed sheets due to their superposed relationship.
A number of attempts have been made to provide double sheet separation along a paper transport route without having obtained complete success. For example, one prior method is shown in U.S. Pat. No. 3,504,911 where first and second opposed plate members form a passageway through which sheets are advanced along a path of travel. Port means are laterally positioned in the plate members to distribute applied vacuum within the passageway, the port means being longitudinally positioned proximate to the exit of the plate members to provide an area of high pneumatic resistance within the passageway between the entrance thereof and the port means, and an area of low pneumatic resistance within the passageway between the exit thereof and the port means. A vacuum is applied to the passageway through the port means via a manifold connected to a supply source. As a result of this high pneumatic resistance at the entrance end, air enters the passageway through the exit end in response to the vacuum pressure to separate superposed sheets located therein.
In another attempt at superposed sheet separation, U.S. Pat. No. 3,040,866 discloses a vacuum separation device used in a conveying system. Two belts having vacuum ports are initially opposed close together in a parallel arrangement and are then guided farther apart thereby creating a separating force for doublets as the opposed members of the doublets are attached by vacuum force to the opposed belts which become increasingly further apart. Yet another doublet separating device is shown in U.S. Pat. No. 3,674,257 where two opposed plates have rows of vacuum apertures. The bottom plate has a plurality of guides in line with the apertures which intercept the path of travel along a portion of the plate face area so that the advancing sheets are raised from the lower face toward the upper face thereby putting the upper sheet of the doublet into position to be picked up by the vacuum apertures of the upper face while the lower sheet of the doublet remains attached to the lower vacuum apertures, thus bringing about separation of doublets. IBM Technical Disclosure Bulletin, Vol. 6, No. 8, January 1964, pages 17, 18 shows a double sheet detector that employs vacuum means to separate sheets.
A major disadvantage of the previously described doublet separators has been their ineffectiveness in handling a wide variety of sheet porosities, sheet overlapping relationships and the tendancy of sheets to feed in slugs.